The present invention is concerned with a process for the production of cellulose fibres by extruding a solution of cellulose in a substantially aqueous tertiary amine-oxide through spinning holes of a spinneret into filaments and conducting the extruded filaments across an air gap into a precipitation bath.
As an alternative to the viscose process, in recent years there has been described a number of processes in which cellulose, without derivatization, is dissolved in an organic solvent, a combination of an organic solvent and an inorganic salt, or in aqueous salt solutions. Cellulose fibres made from such solutions have received by BISFA (The International Bureau for the Standardisation of man made Fibres) the generic name Lyocell. As Lyocell, BISFA defines a cellulose fibre obtained by a spinning process from an organic solvent. By "organic solvent", BISFA understands a mixture of an organic chemical and water. "Solvent-spinning" is considered to mean dissolving and spinning without derivatization. So far, however, only one process for the production of a cellulose fibre of the Lyocell type has achieved industrial-scale realization. In this process, N-methylmorpholine-N-oxide (NMMO) is used as a solvent. Such a process is described for instance in U.S. Pat. No. 4,246,221 and provides fibres which present high tensile strength, high wet-modulus and high loop strength. A process for the industrial-scale production of spinnable solutions of cellulose in tertiary amine-oxides is known from EP-A - 0 356 419.
However, the usefulness of plane fibre assemblies, for example fabrics, made from the fibres mentioned above, is significantly restricted by the pronounced tendency of the fibres to fibrillate when wet. Fibrillation means the breaking up of the fibre in longitudinal direction at mechanical stress in a wet condition, so that the fibre gets hairy, furry. A fabric made from these fibres and dyed significantly loses colour intensity as it is washed several times. Additionally, light stripes are formed at abrasion and crease edges. The reason for fibrillation may be that the fibres consist of fibrils which are arranged in the longitudinal direction of the fibre axis and that there is only little crosslinking between these.
WO 92/14871 describes a process for the production of a fibre having a reduced tendency to fibrillation. The reduced tendency to fibrillation is attained by providing all the baths with which the fibre is contacted before the first drying with a maximum pH value of 8.5.
WO 92/07124 also describes a process for the production of a fibre having a reduced tendency to fibrillation, according to which the never dried fibre is treated with a cationic polymer. As such a polymer, a polymer with imidazole and azetidine groups is mentioned. Additionally, there may be carried out a treatment with an emulsifiable polymer, such as polyethylene or polyvinylacetate, or a crosslinking with glyoxal.
In a lecture given by S. Mortimer at the CELLUCON conference held in 1993 in Lund, Sweden, it was mentioned that the tendency to fibrillation increases as drawing is increased.
It has been shown that the known cellulose fibres of the Lyocell type still leave something to be desired in terms of tendency to fibrillation, and thus it is the object of the present invention to provide a cellulose fibre of the Lyocell type having a further reduced tendency to fibrillation.